Photometer.



TROY L. PARKER, or cmcaso, rumors.

PHOTOMETER.

Speciflcation of Letters Patent.

Application filed November 15, 1915. Serial No. 61,496. I

object is to provide means for directly indi I eating by observation ofthe user the suitable time for exposure of photographic films and thelike. Another object is to provide a photometer which shall be compact,accurate and self-contained, and which can be used by the operator toget readings in any suitable way Without the necessity of any additionalapparatus or special preparation. Other objects will appear from time totime in the specification. My invention is illustrated in theaccompanying drawings wherein,

Figure l is a side elevation showing the photometer in the extendedposition ready for operation.

Fig. 2 is a longitudinal section on an enlarged scale.

Fig. 3 is a section along the line 3-3 of Fig.1.

Fig. 4 is a side elevation of the shutter itself.

Fig. 5 a longitudinal section through the shutter showing a modifiedarrangement.

Fig. 6 is a section along the line 6 6 of Fig. 5.

Like parts are indicated by similar l'etters in all the figures.

A is a.cylindrical barrel. It is necked down at one end as at A to aninternal diameter slightly smaller than the internal diameter of theremainder thereof. Immediately adjacent the necked down portion andprojecting from the cylinder barrel roper is a knurled or roughenedcollar A he wall of the cylinder A is provided with a triangularaperture A having one side parallel with the axis of the cylinder. Alongthat side is arranged a scale A calibrated as indicated in timeintervals, in this case preferably calibrated for time intervalsnecessary tograph1c film, though obviously it might be calibrated on anysuitable basis. The triangular aperture, it willbe noted, in-

' and tube.

for the proper exposure of a phocreases toward the lower end of thecylinder where it is bounded by a side wall at right angles to the longcalibrated wall. The third side wall is a spiral as indicated.

B is a hollow tube slidably mounted in the necked down portion of thecylinder A the bearing surface between the two being suflicient to holdthe tube at all times and in all ositions in parallelism with thecylinder an to prevent rocking or tipping of the tube with respectto thecylinder. B is a Patented Aug. 20, 1918.

truncated conical eyepiece provided at its inner end with a reducedcylindrical portion B engaging the interior of the tube B and heldtherein by any. suitable means not here specifically indicated. Thisreduced portion has the cross wall B apertured for vision at B on thecommon axis of cylinder B is a disk perforateat B in line with theperforation B*. This disk is thrust into the opposed end 'of the tube Band expands it as indicated sufficiently to prevent complete withdrawalof the tube from the reduced portion of the cylinder.

C is a cylindrical shutter. It is rotatably mounted inside the cylinderA. It is provided at its bottom with knurled or roughened collar Cadapted to project upwardly beyond the surface of the cylinder A. The

bottom of this shutter is closed as at C and contains a disk C uponwhich is a suitable object such as the cross C. In my preferred form thedisk is white and the crossblack, so as to be clearly visible. Theeffective edge ofthe shutter is a spiral as indicated at-C. Thusimmediately above the the aperture in the cylinder A. This narrowextension of the shutter is provided with a lug C which engages a grooveC in the interior of the cylinder A whereby the shutter when once'thrust into the cylinder, is held therein b the yielding ressure of theshutter, which yieldingly holds the lug in the groove.

D is a translucent cylinder or screen. It

-is carried by and in a sense forms part of the shutter and preferablyis located within it though it might abut against it if that provedesirable. This cylinder is more or less opaque, and tends more or lessto ohstructthe passage of light rays into the interior of theinstrument. This cylinder closes up and keeps the sleeve always closedso as to prevent too intense illumination and I so as to control theoperation of the device.

It will be evident that while I have shown in my drawings an operativedevice, still many changes might be made in size, shape and'arrangementof parts without departing from the spirit of my invention.

The use and operation of my invention are as follows The operator, whoexpects either to measure the intensity of the light where he tands orelse to determine the time during which he must expose his photographicfilm or plate in order to take a picture, starts with the eye-piece inthe position shownin dotted lines in Fig. 1.. At that time the shutterwould preferably be in such position as to completely close thetriangular aperture in the cylinder. lheoperator then draws the eyepieceand tube out into the position shown' in Fig. 2. He rotates the shutterun til the aperture in the cylinder is completely open. He thenapproaches the place at which he wishes to make the determination. If heis going to take a picture, he wants to find the intensity of the lightfalling upon the object to be photographed, and so heapproaches theobject which he wishes to photograph. He stands facing the brightestlight with the instrument in his hand and points it toward the light,holding it in a substantially horizontal plane with the aperture in thecylinder open upwardly so that light falls in the cylinder. He applieshis eye closely to the eyepiece and looking through, sees the blackcross on the white ground. By rotating the shutter in a clock wisedirection, he' gradually closes the triangular aperture in the wall ofthe cylinder, thus decreasing the amount of light falling on the objectcross. This rotation will be continued until the v.cross becomesinvisible,

or barely visible as suits his eye- At that point he stops rotation ofthe shutter, and reads on the scale on the cylinder the time forexposure indicated where the diagonal wall of the shutter crosses thescale. lit will be understood that the eye is closely applied to theeyepiece in order to completely exclude the light around the eyepiece.It will also be understood that if for any reason the operator can nothimself go to and stand by the thing which he wishes to photograph, hewill still be able to get a reading by going to a place Where the lightconditions appear to be about the same as those prevalent about theobject to be photographed.

For the sake of illustration, we will assume that the operator has madehis observation and he finds that the shutter has moved until theboundary wall occupies the position shown in dotted lines in Fig. 1.That Latc es wall cuts the index side between ten and twenty fiveseconds. He makes the necessary mental calculation and reads say fifteenseconds. This is the time he must expose his film if his lens is open ata sixteen diaphragm If the lens is open wider or not so wide, he mustchange the time accordingly. In other words, I have selected the sixteendiaphragm because the sixteen opening is common to a number of lensopening or aperture scales. If instead of wishing to operate at sixteen,he wishes to operate at a larger aperture, say, eight, which on theUnited States scale means a diaphragm of twice the effective opening, hewill divide his reading of fifteen seconds by half, expose his filmseven and a half seconds. If, on the other hand, he wishes to close downto one half the opening, he will multiply his reading by two and exposehis film in fifteen to thirty seconds. It will be understood that directsunlight must not be allowed to impinge upon the object disk, and theoperator by carefully manipulating the device, can avoid this. However,in order to insure that only direct modified illumination shall beallowed to act upon the disk, ll provide the translucent cylinder withinthe shutter. This may take the form of paper, glass, celluloid or anyother suitable material as indicated. lit permits the light to passthrough, but does not permit the free unobstructed sunlight to fallthrough to the disk even if the instrument were improperly held. It willbe understood that for difi'erent purposes, cylinders of differentquality might be used. For very bright work in the tropics, a very darkcolored cylinder would be used. For work in dark places,- a lightercylinder might be used. lit will be understood that different types ofphotographic work and plates and films having different subjects are inuse, and my device may be conveniently adapted for such purposes byusing different kinds of screen cylinders, so that the reading ismodified according to the peculiar uses to which any particularinstrument is to be put. It will be understood that the size of theapertures in the two disks or transverse walls at either end of theeyepiece carrying tube may vary. llt is desirable, however, that theirproportionate sizes be such that the line or sight as the operator hashis eye in WEB the eyepiece and looks inwardly toward the wouldotherwise be reflected into the eye of the operator, and thus interferewith the accuracy of the reading made by him. It will be noted that theaperture through the .farther disk is provided with counter sunk orconical sides, so that there may be no possible chance of any reflectionof light rays into the eye of the operator by the wall of the hole. Theinner edge is sharp and cannot therefore well reflect any appreciablequantity of light.

The photometer is thus divided into an illumination chamber with alightwindow in the wall thereof, a visual object therein, and means forcontrolling the efi'ect-ive opening of the window, and an eyepieceremoved from the illumination chamber but connected to it by alight-tight casing which casing is provided with means for prevent ingreflection of light from the illuminating chamber into the eyepiece bythe walls thereof, thus the only light rays reaching the eye of theoperator must come direct from the illumination chamber and cannot bereflected by the walls of the connection into the eye of the operator.

It will be understood that preferably the entire interiorof theinstrument will be black, of a dead, dull finish, in order that if byany chance any uncontrolled light rays do enter, they will be absorbedand not reflected. The shield which may take the form of the perforatepartition or of the cylinder in the shutter being interposed in bothcases between the object and the source of light, operates in part toprevent the impingement on the eye-piece of any light rays except thosereflected from the object, and it will be observed that the perforatepartition and the colored cylinder are for this purpose at leastequivalent since whatever may be their separate functions, each one ofthem will have this specific function.

While the apertured partition and the translucent cylinder or diaphragmare equivalent for some purposes it is evident that under certaincircumstances it is desirable to use them both in the same machine andunder some circumstances they would cooperate to produce the sameresult. Most cylinders of different color or different thickness wouldvery obviously have varying effects on the reflected light rays and onthe intensity of illumination so that by changes in the size of theaperture in the plug or wall and by changes in the color of thethickness of the diaphragm, a desired combination may be obtained.

I claim:

1. A photometer comprising a single opaque visual object, means for.controlling the illumination thereof, an eye piece removed from saidobject and means for preventing the entrance into said eye-piece of anylight rays except those coming directly from the ob]ect.

2. A photometer comprising a single opaque visual object, means forcontrolling the illumination thereof, an eye-piece removed from saidobject and means for preventing the entrance into said eye-piece of anylight rays except those coming directly fromthe object, said meanscomprising an apertured partition interposed between the eye-piece andthe object.

3. A photometer comprising a single.

opa no visual object, an illumination chamber m which it is contained,means for controlling .the illumination of the object by varying theamount of light entering the chamber, an eye-piece removed from thechamber and means for excluding from the eyepiece any light rays exceptthose reflected by the object.

4. In an optical instrument a supporting sleeve, a tube slidable thereinthe sleeve be ing provided with a bearing for the tube,

an eye piece mounted in one end of the tube larger than the bearing inthe sleeve, a perforated plug mounted in the other end of the tubelarger than the normal interior diameter of the tube and adapted toexpand the tube to an outer diameter larger than the diameter of thebearing the perforations in the eye piece and in the plug beingconcentrio and in line with the axis of the tube.

5. In a photometer a single illumination chamber, an opaque visualobject therein the wall of the chamber being perforated, a shuttermounted for movement within the chamber across such perforation and atranslucent difiusingscreen carried by said shutv ter mounted formovement within said chamber and adapted always to extend across thatpart of the perforation in the chamber wall which may be uncovered bythe shutter and an eye piece in line with the visual object.

In testimony whereof, I afiix my signature in the presence of twowitnesses this 10th day of November, 1915.

TROY L. PARKER.

Witnesses:

ESTHER VAN FRANK, CHRISTINA DEANS.

